Everyone has one. That campaign that was an absolutely amazing idea, but it either didn't get started or it only ran a few sessions and fell apart. Maybe you ran it. Maybe you played in it. Today I wax nostalgic on some of the campaigns that got away.
As a GM:
-Legacy of Dracula: A GURPS steampunk/horror game pretty much entirely inspired by Kim Newman's novel, Anno Dracula. Failed four sessions in when I realized that I hate GURPS.
-Age of Gears, my Savage Worlds "steampunk ghostbusters" game. The schedules of the three ladies playing simply weren't compatible and we never continued after the ladies solved the case of Spring-Heeled Jack. (So at least we had some closure there.)
As a player:
-In college, my pal Glenn ran a Vampire: the Dark ages chronicle. Or tried, to, at least. He did a lot of research and preparation, and the rest of the group basically turned it into D&D at nighttime with fangs. He threw up his hands and quit about one session in. (Disclaimer: My character was totally appropriate for the setting. I did research, dammit.)
-My wife ran a World of Darkness game that only lasted one session. One of the players creeped my wife out with his constant emails and contacts, so she canceled the game because the experience left a bad taste in her mouth. It's too bad, because I loved the cast of characters in that game.
-My wife ran a post-apocalyptic World of Darkness game about survivors trying to figure out what happened and finding a community. There was mystery, supernatural mystery, and fantastic NPCs. The game fell apart because one player was a dick and my wife couldn't stand him anymore. Plus, my wife has acknowledged that she's better with one-shots and short games than she is with long campaigns. I'll never know what happened to the world, or what happened to my character's NPC wife. Also, my character was based on a dude I sat next to on a bus once.
So, what's your "one that got away?"